1. Field of the Invention
The present invention relates generally to standby power systems for supplying power to a supported system or device, such as a computer or telephone switching equipment when an AC (alternating current) normal operating supply has a power outage or the AC line voltage drops below a predetermined and adjustable minimum voltage. More particularly, the present invention relates to an external backup power system for supplying DC (direct current) backup power without requiring modification of the supported device.
2. Description of the Prior Art
Backup power systems are increasingly used for applications, such as computer, security, data processing and communications equipment to avoid interruptions resulting from a primary AC power source. Various arrangements have been employed to provide a backup or standby power supply.
Standby supply systems are disclosed in U.S. Pat. Nos. 3,790,822; 4,401,895; 4,327,298; 4,313,060; 4,362,951; 4,366,389; 4,395,639; 4,400,626; 4,647,787; 4,468,571 and 4,885,521. Disadvantages of the known arrangements include complexity, expense and unreliability. Many of the known arrangements require modifications and/or direct wiring interconnections within the power supply circuit of the supported device, such as disclosed by U.S. Pat. Nos. 4,401,895; 4,327,298 and 4,885,521.
U.S. Pat. No. 4,313,060 discloses a continuous-type uninterruptible power supply including a controlled ferroresonant regulator and rectifier combination supplying independent DC outputs and driving an inverter. The inverter is arranged to provide a plurality of AC and DC outputs.
U.S. Pat. No. 4,885,521 discloses a supplemental battery backup power system for computer systems that, in the absence of AC line voltage, supplies DC voltages directly to the computer DC power bus and by-passes the internal, AC, computer power supply. A special harness assembly connects the supplemental battery backup power system with a personal computer. The harness assembly must be adapted for an output array of voltages and currents in a specific, physical arrangement of a power input connector for a specific computer processing unit to which the backup power is supplied.
It is desirable to provide an external backup power system capable of simply and effectively supplying DC (direct current) backup power to a supported device without requiring any modification of the supported device. It is important to provide such backup power supply that can be used with a various devices and that is inexpensive.